I understand that you dislike the Hank Pym character and find him unnecessary, and would prefer him not to be a featured character in the MCU. That is well and good... arguing personal preference is a waste of time. However, we know that the Ant Man movie IS coming, and will be kicking off Phase III.

With this in mind, wouldn't it be more rational to associate the Ultron story arc with Hank Pym/Jan over Stark? Wouldn't the Ultron association add a plenty of texture and richness to the former (Pym/Jan) story arc, while being somewhat superfluous to the latter (Stark)?

Yes, the comics are not the holy grail, and where necessary, things can (and should) be tweaked to better suit the movies. However, in my opinion, a tweak of this nature is not only unnecessary, it would be counter-productive in the grand scheme of things.